This invention relates to an ultrasound system and method for three-dimensional imaging. In particular, a method and system for controlling opacity for three-dimensional images is provided.
Ultrasound data for various modes of operation are typically used to generate one or more images. Conventional modes of operation include B-mode, color Doppler, Doppler Tissue Motion (see U.S. Pat. No. Re. 35,720) and others.
For three-dimensional imaging, scan converted data used to generate a two-dimensional image may be output to a separate processor or computer. The computer arranges a plurality of sets of data representing two dimensions into a data set representing three-dimensions. Alternatively, a two-dimensional array is used to directly acquire a 3D data set. The data is coded as color or RGB values. A three-dimensional representation is then rendered.
In order to represent the three-dimensional (3D) data set, a two dimensional (2D) image is rendered. For example, a minimum or maximum projection value is displayed. Data along ray lines normal to a viewing plane are compared. The maximum or minimum value along each ray line is displayed opaquely and the other values are translucent (i.e. not displayed).
As another example, each datum is assigned an opacity level corresponding to B-mode intensity, a fixed value, or as a function of depth. The RGB values of each datum are summed as a function of opacity along viewing lines into the 3D data set. However, the relative opacity of various data does not advantageously emphasize some data and de-emphasize other data.
P. L. Carson et al. disclose a "two-dimensional projection of the 3D data [FIG. 5A] in which the depth cue is obtained by decreasing the gray scale pixel brightness as a function of depth (termed `opacity`) along a line of site [sic]. The color pixels representing flow are made completely opaque to maintain maximum flow information." See Enhanced Color Flow Imaging of Breast Cancer Vasculature: Continuous Wave Doppler and Three-Dimensional Display, J. Ultrasound Med. 11:377-385 at 382, 1992. Also regarding FIG. 5A, the hue is set based on the Doppler Frequency shifts. See page 384. Carson et al. make a brief statement at page 381 that brightness, hue, saturation, ray attenuation and opacity, and other characteristics were assigned as a function of gray scale pulse echo amplitude and Doppler color (frequency shift signal). This statement is followed by the example for FIG. 5A discussed above.